Disclosure of a stem cell phenotype in an oral squamous cell carcinoma cell line induced by BMP-4 via an epithelial-mesenchymal transition

A small subset of cells within a malignant neoplasm, named cancer stem cells (CSCs) or tumour initiating cells, are thought to be capable of initiating the neoplasm itself, and of driving its growth and recurrence after treatment. It is unclear whether CSCs can be identified and experimentally induced within oral squamous cell carcinoma (OSCC), although this has been reported for a number of other tumour types. In this study, we aimed to determine whether BMP-4 (bone morphogenetic protein-4) could induce epithelial-mesenchymal transition (EMT) with acquisition of stem cell-like phenotypes in a cell-culture model. Furthermore, the differential expression of ABCG2, a putative CSC marker, was determined in human normal oral mucosa and OSCC tissues at mRNA and protein level. The results showed that after treatment with BMP-4, most Tca8113 cells (a human tongue OSCC cell line) changed their morphology from slabstone to spindle-shaped, and demonstrated enhanced expression of ABCG2 compared with non-treated cells. Expression of Oct-4 was induced in cell nuclei with up-regulation of EMT markers (Snail, Slug and vimentin), and down-regulation of E-cadherin. Interestingly, the expression of hTERT, CD44 and Bmi-1 (generally accepted as markers of CSCs) were up-regulated, but this was not synchronous with the expression of EMT markers. Tumour spheres were formed after stimulation with BMP-4, with high expression of CD44 and ABCG2. In human tissues, ABCG2 was strongly expressed in OSCC, but not in normal mucosa. This study suggests that BMP-4-mediated EMT constitutes one possible pathway for the development of CSCs in oral cancer, implying a transient therapeutic opportunity if EMT can be interrupted early in the evolution of such a neoplasm.